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Continuous soil gas radon monitoring in real time with improved solidstate detector is carried out in south-central and southern Taiwan. The time series register spike-like anomalies which could be precursors of earthquakes. Monitoring stations located in a brecciated zone of active fault at Taiwan 3 and faults at Taiwan 1 showed drastic variations of radon when the terrain is stressed before the onset of earthquake. In contrast, the spectrum recorded at a station sited on a craton Akron 1 which is sited on a craton shows no significant radon variations. To actually prove that the variation of the time series is related to stress, a fourth station was anchored in a sand column (209 L) with exactly the same type of radon detector system. The time series recorded in this manner shows higher background level and spikes of high radon counts as it is stressed. Temperature and moisture variations are not affecting radon counts.

Gas variations of many mud volcanoes and hot springs distributed along the tectonic sutures in southwestern Taiwan are considered to be sensitive to the earthquake activity. Therefore, a multi-parameter automatic gas station was built on the bank of one of the largest mud-pools at an active fault zone of southwestern Taiwan, for continuous monitoring of CO 2 , CH 4 , N 2 and H 2 O, the major constituents of its bubbling gases. During the year round monitoring from October 2001 to October 2002, the gas composition, especially, CH 4 and CO 2 , of the mud pool showed significant variations. Taking the CO 2 /CH 4 ratio as the main indicator, anomalous variations can be recognized from a few days to a few weeks before earthquakes and correlated well with those with a local magnitude >4.0 and local intensities >2. It is concluded that the gas composition in the area is sensitive to the local crustal stress/ strain and is worthy to conduct real-time monitoring for the seismo-geochemical precursors.

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